JP2010017809A - Method and device for electrical discharge machining of small-diameter tapered hole - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for boring a hole having a circular, elliptic, or elongated shape and tapered in a horn shape by electrical discharge machining using a small-diameter electrode. <P>SOLUTION: In this electric discharge machining, a C-axis table on which a workpiece is placed, an XY-axis stage, and a Z-axis electrode head are numerically controlled in synchronism with each other. The Z-axis electrode head includes an axially feeding device and a mechanism for tilting the axial direction in one plane. The distance between the designated boring point of the workpiece attached to the C-axis table and the center of the C-axis table is set at R. While moving the Z-axis feeding device by a reciprocating shuttle motion, the circular tapered hole having a profile cross section of horn shape is electrical discharge-machined by synthesizing the synchronous motions calculated by using the swing angle θ of a C-axis and the following formulas [expression 2], [expression 3], or [expression 4] of the XY stage. The formula [expression 2]: Ci=θi, Xi=Rsinθi, Yi=Rcosθ, the formula [expression 3]: Ci=θi, Xi=Rsinθi, Yi=Rcosθi+β, and the formula [expression 4]: Ci=θi, Xi=Rsinθi, Yi=Rcosθi+qi. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

The present invention relates to NC electric discharge machining, and relates to machining of fine pores and fine-shaped NC electric discharge machining. More specifically, the present invention relates to a non-rotating, small-diameter cantilever supporting electrode, and a round hole or irregular shape on a workpiece. The present invention relates to a technique for drilling a hole having a contour cross section, further processing an electrode by inclining, and expanding the contour cross section in a tapered shape.

The fuel injection nozzle is made of a metal that can withstand high temperatures and has a small nozzle hole, so electric discharge machining, laser machining, and the like are more suitable than cutting.
In a fuel injection nozzle of a certain type of internal combustion engine, not only a straight hole having a uniform cross section such as a cylindrical shape, an ellipse, or an ellipse, but also a fuel introduction like a nozzle body cross section of FIGS. The taper shape which expanded the part from the ejection part may be calculated | required. Since the nozzle body is cylindrical and the internal space is narrow, the drilling of the taper extending from the outside to the inside can be performed only with the thin electrode from the outside.

For example, (Patent Document 1) discloses an example in which the cross-sectional contour shape of the injection passage of the injection nozzle of the internal combustion engine is non-circular and the contour cross-section is enlarged in a trumpet shape. Describes a method of processing a conical shape by applying a magnetic field from the electrode side surface and utilizing electrode deflection caused by Lorentz force.

In response to recent demands for improving the fuel consumption rate of internal combustion engines, the freedom of design shape and dimensional accuracy play an important role in improving injection nozzles. Proposed method of pore machining by non-rotating pipe electrode (Patent Document 2), NC drilling electric discharge machining method by wire electrode line (Patent Document 3), numerically controlled single cutting tool contour machining method (Patent Document 4), etc. .

JP 2007-263114 A JP 2007-260878 A JP 2008-834 A JP 2007-18495 A

The fuel injection nozzle is a small-diameter hole, but in order to reduce fluid resistance and to obtain a spray effect, the passage length is shortened, the cross-section is circular or non-circular, and the cross-sectional area is changed to a trumpet shape. Various ingenuity is given. Even in this case, since the cross section of the injection port is required to have a small diameter, it is difficult to perform normal cutting, and electric discharge plays a role.

In electrical discharge machining, it was necessary to rotate the electrode in order to process the pores with a small-diameter electrode. However, since the electrode rotation is difficult in terms of device rotation, the rotation of the workpiece and the circular interpolation motion of the electrode in the XY plane The present inventor has proposed a method of moving the workpiece and the electrode relative to each other by synthesis. Specifically, the electrode side has an XY NC control axis, and performs simultaneous biaxial interpolation in the XY plane. When the workpiece is mounted on the C-axis table and swung at a constant speed, and the electrode is made to follow the fixed point P of the workpiece by simultaneous biaxial interpolation, the electrode and the machining point move relative to each other. Thus, it is a basic principle of the present invention to perform electric discharge machining while rotating the machining point relative to the small-diameter electrode.

In the electric discharge machining in which a C-axis table on which a workpiece is placed, an XY-axis stage, and a Z-axis electrode head are synchronously controlled by the NC, the Z-axis electrode head includes an electrode axial feed device and a single axial direction. A tilting mechanism for tilting in a plane is provided, and a drilling specified point P specified for the workpiece when the workpiece is attached to the C-axis table is at an arbitrary distance (R) from the center O of the C-axis table, Also, it is mounted in such a posture that the direction of the Z axis coincides with the direction of the hole, and the reciprocating shuttle motion of the electrode feeding device is performed, and the C axis rotation (θ) and the XY axis stage equation “Equation 2”, or 3 ”or the synthesis of the synchronous motion calculated by the formula“ Equation 4 ”realizes electric discharge machining of a tapered hole such as a circle, an ellipse, or an oval having a trumpet outline.
"Number 2"
Ci = θi, Xi = Rsinθi, Yi = Rcosθ
"Equation 3"
Ci = θi, Xi = Rsinθi, Yi = Rcosθi + β, where β is a constant.
"Equation 4"
Ci = θi, Xi = Rsinθi, Yi = Rcosθi + qi, where qi is a variable that determines the cross-sectional shape of the hole.

In the present invention, a tapered hole is processed, but it is obvious that the electrode side may be inclined for this purpose. However, since drilling cannot be performed by the Z-axis motion, it is necessary to cause the electrode feeding device to perform a reciprocating shuttle motion.
Further, the present invention achieves the object by providing an apparatus that sequentially executes initial hole machining, tilt angle machining, and lateral servo contour machining in carrying out the electric discharge machining method described in the preceding paragraph [0008].

In the present invention, a taper function and an electrode shuttle motion function are added to the one proposed by the present inventors in the aforementioned Patent Documents 2, 3, and 4 as an electric discharge machining method for relatively rotating an electrode and a workpiece. It solves the problem of electric discharge machining accompanying taper machining.

As a precaution, the taper hole machining proposed by the present invention is compared with other methods as follows. There are two types of rotation of the electrode and the workpiece: work turning (lathe method) and tool turning (drilling method). The former is suitable for long holes such as barrels and cylinders and high-precision machining, but is inconvenient for positioning, and is not suitable for machining a large number of holes, and the latter is the opposite. Tool turning is mainly used in micro-hole electrical discharge machining, but there are difficulties in energization and liquid flow. The system of the present invention does not belong to any of the above two types, and solves any difficulty.

The “method of performing electrical discharge machining by relatively rotating an electrode and a workpiece” described in the previous stage, which is the basis of the present invention, refers to an electrode at a specified point P of a workpiece on a C-axis table installed on an XY table. If the center O is aligned and the C axis is swiveled, and the X and Y axes are made to follow the C axis swivel by applying an arc interpolation motion according to the formula “Equation 2”, the electrode will be stationary with respect to the XY machine coordinate system. However, it rotates on the point P of the workpiece coordinates. At this time, if the electrode axis is inclined, a tapered hole is processed.

Then, when an electric discharge machining voltage is applied and axial servo feed is applied, a hole having a circular cross section with an electrode diameter is turned and punched. If the radius of the circle to be drilled is enlarged by β, Yi = Rcosθi + β may be set as shown in the expression “Equation 3”. Further, in order to obtain a non-circular shape such as a circle or an ellipse in the cross section of the hole to be drilled, the radius (qi) from a fixed point in the figure to be obtained is obtained as shown in FIG. = Rcosθi + qi.

The effect of rotating the electrode and the workpiece relative to each other by the method of the present invention prevents the electrode from being bent, eliminates the need for an electrode rotating mechanism, and simplifies the means for energization / fluidization, thereby reducing the size of the apparatus. Moreover, the positioning of the rotation center and the processing point, which has been a drawback of the general work turning method, is simplified by the NC function, and thus has many advantages.
However, since electrode wear cannot be ignored, axial shuttle movement of the electrodes is necessary to compensate for electrode wear.

The electric discharge machining of the taper hole expanding in a trumpet shape is performed by combining the rotation of the rotary table and the NC circular interpolation motion described in the principle diagram of FIG. 4A or FIG. This is made possible by the relative movement of the points and the tilting function of the electrode axis, but the problems to be solved are as follows.

As shown in FIG. 7 (a), in the machining of the tapered portion, it is unsuitable as an electric discharge machining control method to advance the machining in the electrode feed direction (U) and at the same time the machining in the electrode side surface direction (V). This is because when the short circuit or the arc is detected, the retreat direction is unknown, so that it is distorted and cannot return to a normal machining state.

Therefore, the method that can be selected is either the electrode feed direction (U) or the electrode side surface direction (V). In the present specification, the former is called an axis servo and the latter is called a lateral servo.

In the case of the trumpet-shaped processing, which is a problem, the lateral servo is in two directions. One is the circumferential direction, which is the horizontal servo contour machining, and the other is the machining that cuts the inclination angle in the radial direction.

The optimum processing sequence is to first process an upright hole having a uniform cross section without a taper at the center of the hole. Next, the electrode is processed to an angle (α ₀ ) while being inclined. After that, lateral servo processing is performed in the circumferential direction while maintaining the angle (α ₀ ).

When the desired angle is (α ₀ ), in order to remove the leftover due to electrode wear and electrode rigidity, the process is completed after several rounds.

As shown in FIG. 7B, the angle (α ₀ ) is considered from the relationship between the maximum dimension of the removed portion (1/2 of the difference in the aperture diameter), the diameter (d) of the electrode 10 and the electrode consumption. It should be. When 1/2 of the hole diameter difference is larger than the diameter (d) of the electrode 10, the value of (α ₀ ) is divided,
Formula (1) (α ₀ ) = (α ₁ ) + (α ₂ ) + (α ₃ ) + (αn)
The processing steps are repeated n times.

The reason for having to repeat the processing step is not only the difference in the diameter, but also because the electrode must have a low rigidity and the best choice because of the limitation to use a thin electrode with a cantilever support. This is because wear cannot be ignored.

The apparatus of the present invention is configured as follows. FIG. 1 is an explanatory diagram of the whole, and is an NC electric discharge machining apparatus in which a C-axis table 2 on which a workpiece 1 is mounted, an X-axis stage 3, a Y-axis stage 4, and a Z-axis head 5 are synchronously controlled by an NC. Are attached to the front surface of the Z-axis head 5 with the boss 8 as a fulcrum and freely tilted. The tilt mechanism 8a causes the motor 14 to tilt the electrode head 6 with respect to the Z axis.
The electrode head 6 is provided with an electrode axial feed device 7, and the action of the motor 15 and the roller set 16 causes the electrode 10 to move in the axial direction, or to perform electric discharge machining, or to perform an axial shuttle motion.

The apparatus described in the preceding paragraph [0023] operates as follows in the initial hole machining.
The initial hole machining is a process of forming a hole having a uniform cross section such as a circle, an ellipse, or an ellipse having a required shape into a specified position and direction of the workpiece 1 by means of a pore discharge process. 10 is inserted into the workpiece 1 to prepare for lateral servo.

As shown in FIGS. 6A and 6B, the workpiece 1 is attached at an arbitrary position, but the jig 11 (see FIG. 6) is arranged so that the designated direction (injection direction) of the hole is the Z-axis direction. It is necessary to determine the posture using 1) or the like. The distance R between the hole position and the C-axis center O is easily measured by NC operation.
The electrode tip is positioned at a specified point, and as shown in FIGS. 4A and 4B, the distance R from the C-axis center O is given as a constant to the NC device. 3 ”or the expression“ Equation 4 ”.

In the initial hole processing, as shown in FIGS. 1 and 2, the axial direction of the electrode 10 coincides with the Z-axis direction. In order to carry out the electric discharge machining, it is possible to make the electric discharge machining servo feed by utilizing the Z-axis motion and the function of the electrode feeding device 7, and the selection is free.

If a swivel motion is given to the C-axis table 2 and NC control is performed on the motions of the XY-axis stages 3 and 4 in accordance with the expression “Equation 2”, an electric discharge machining servo feed is added, and an initial hole having a circular cross section penetrates.

Following the initial hole processing, in order to finish the contour shape, the contour processing is performed with the electrode penetrated. A shuttle motion in the electrode axis direction may be added. When the contour shape is a circle having a radius of (electrode radius + machining gap), the movement of the following expression “Equation 2” is commanded to the XY stages 3 and 4 in synchronization with the turning of the C-axis table 2.
Expression “Equation 2” Ci = θi, Xi = Rsinθi, Yi = Rcosθi

When the radius of the contour shape is a circle of (electrode radius + β + machining gap), the movement of the following formula “Equation 3” is commanded to the XY stages 3 and 4 in synchronization with the turning of the C-axis table 2.
Formula “Equation 3” Ci = θi, Xi = Rsinθi, Yi = Rcosθi + β, where β is a constant.

When the contour shape is a non-circular shape such as an ellipse or an ellipse, a fixed point A is defined inside the contour figure as shown in FIGS. 5A and 5B, and the radius q to the contour line is set as the polar coordinate origin. And θ are obtained over the entire circumference, and the relationship between θi and qi is given by the following equation (Equation 4).
Formula [Equation 4] Ci = θi, Xi = Rsinθi, Yi = Rcosθi + qi, where qi is a variable that determines the cross-sectional shape of the hole.
As a result, in synchronization with the turning of the C-axis table 2, the movement of the expression “Equation 4” is commanded to the XY stages 3 and 4, and the inner diameter of the figure to be obtained is processed. However, the machining gap is enlarged.

When the initial hole is processed, the process proceeds to tilt angle processing. Inclination angle machining is electric discharge machining in which an electrode 10 is inserted into an initial hole to be inclined. The Z-axis electrode head 5 is moved, the center height (S) of the inclined fulcrum boss 8 in FIG. 1 is adjusted to the upper surface (L) of the workpiece, the electrode is inserted into the initial hole, and reciprocates to the electrode feeder 7. The electrical discharge machining voltage is applied by causing the shuttle motion, and the electrical discharge machining is performed by gradually adding the operation of the tilt mechanism 8a to the tilt angle (α). Since the inclination angle is very small, processing proceeds in the same manner as wire electric discharge processing.

After the tilt angle machining is completed, the process moves to the lateral servo contour machining. In the horizontal servo contour machining, the electric discharge machining of a hole such as a circle, an ellipse, or an oval having an opening exit larger than the entrance portion is performed by the electrode feeder 7 while giving a reciprocating shuttle motion to the electrode 10. The horizontal servo electric discharge machining is performed by rotating the C-axis table 2 and adding the synchronous motion of the expression “Equation 2”, the expression “Equation 3”, or the expression “Equation 4” to the XY axis stages 3 and 4. Thereby, the side surface of the initial hole is enlarged in a trumpet shape. As shown in the above equation (1), the final shape is obtained by repeating the inclination angle processing and the lateral servo contour processing while adding the inclination angles α ₁ , α ₂ , α ₃ ,... (Αn).

The center of the tilt fulcrum boss 8, that is, the height (S) of the electrode tilt fulcrum coincides with the upper surface (L) of the workpiece 1, so that it can be ignored when the tilt angle (α) is small. However, the contour expands as shown in FIG. 8 due to the inclination of the electrode. The value (δ) is expressed by the equation “Equation 5” where the electrode radius is (r).
Formula “Formula 5” δ = r {(1 / cos α) −1}

In order to correct δ, the expression “Equation 3” or the expression “Equation 4” is corrected to the expression “Equation 6” or the expression “Equation 7”, respectively.
Formula “Equation 6” Ci = θi, Xi = Rsinθi, Yi = Rcosθi + β−δ, where β> δ.
Expression “Equation 7” Ci = θi, Xi = Rsinθi, Yi = Rcosθi + qi−δ, where qi> δ.

As the electric discharge machining electrode, a material having high rigidity and low electrode consumption is selected. For example, tungsten or cemented carbide.

The machine body in FIG. 1 is a four-axis NC machine tool with X, Y, Z, and C axes, and includes an NC control device, an electric discharge machining power source, and an electrode servo control circuit (not shown). As a whole, it is compact and suitable for desktop use. Although the workpiece 1 held by the jig 11 is a cylindrical nozzle body, it may be a flat plate, and a processing designation point is set at a distance R from the axis of the C-axis table 2. A column 12 and XY stages 3 and 4 are disposed on the base 13.

The Z-axis head 5 moves the electrode head 6 along the Z-axis guide (not shown) of the column 12. The electrode head 6 can be inclined at an inclination angle of ± 45 in one plane with the boss 8 as a fulcrum. The tilting mechanism 8a linearly moves the operating rod 8b with the motor 14 to tilt the electrode head 6, and is NC controlled by a not-shown angular scale and sensor.

The electrode feeding device 7 is provided on the upper surface of the electrode head 6 and moves the electrode 10 in the axial direction in cooperation with the steady guide 9. The electrode feed device 7 is provided with a roller set 16 driven by a motor 15 and is always in pressure contact with the electrode 10, and reciprocates with the axial servo feed motion of the electrode according to the rotation of the motor 15 according to the command of the NC control device. Perform shuttle movement and positioning movement.

The electric discharge machining action is due to a short gap discharge generated by applying a discharge voltage pulse from the electric discharge machining power source to the gap between the workpiece 1 attached to the C-axis table 2 and the electrode 10, and an electrode servo control circuit However, the voltage of the gap between the electrodes is detected, and the electrode 10 is caused to perform a servo feed movement so as to adjust the gap between the poles.

The design of the tilt mechanism has various other modes and is not limited to this embodiment. Also, the design of the electrode feeding device is not limited to this embodiment, and there are various methods such as the pipe electrode method disclosed in Patent Document 2 and the wire electrode method disclosed in Patent Document 3. For the steady rest guide 9, a simple guide bush is illustrated, but a pipe guide may be used as close as possible to the processing tip of the electrode 10.

Although not particularly described, energization of the electrode 10 and the workpiece 1, an insulating method between them, or supply of a working fluid to the gap between them is common to general electric discharge machining techniques.

NC control makes it possible to machine an accurate tapered small-diameter hole, which may be used to improve fuel injection nozzles, paints, chemical spray guns and the like of internal combustion engines.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. The front view of FIG. The front view in which the electrode head was inclined. (A) The principle diagram of a planetary system, explanatory drawing of Formula "Formula 2". (B) The principle diagram of the planetary system, an explanatory diagram of the formula “Equation 3”. (A), (b) In the case of a non-circular cross section, an explanatory diagram of the formula “Equation 4”. The figure which shows the relationship between the attachment attitude | position direction of a workpiece, and a Z-axis, and a workpiece upper surface (L). (A) Explanatory drawing of an axial servo (U) direction and a horizontal servo (V) direction (side surface direction of an electrode). (B) Explanatory drawing of inclination-angle (alpha) and the electrode diameter d. Explanatory drawing of the influence of an electrode inclination.

Explanation of symbols

1 Workpiece
1a Nozzle hole
2 C axis table 3 X stage
4 Y stage
5 Z-axis head
6 Electrode head
7 Electrode feeder
8 Boss 8a Tilting mechanism
8b Working rod
9 Electrode steady rest guide
10 electrodes
11 Jig
12 columns
13 base
14 Inclination mechanism motor
15 Electrode feed motor
16 Electrode feed roller set
(U) Shaft feed direction
(V) Lateral servo direction (S) Center height of boss
(L) Height of workpiece top surface or specified hole start point

Claims (3)

In electrical discharge machining where the C-axis table, XY-axis stage, and Z-axis electrode head on which the workpiece is placed are synchronously NC controlled,
The Z-axis electrode head is provided with an electrode axial feeding device and an inclination mechanism for inclining the axial direction in one plane,
The distance between the specified drilling point P of the workpiece to be attached to the C-axis table and the C-axis table center O is (R),
Also, attach the workpiece in such a posture that the direction of the Z axis and the hole match,
The reciprocating shuttle motion is performed on the electrode axial direction feeding device, and the rotation is calculated by the following equation “Equation 2”, “Equation 3”, or “Equation 4” of the XY axis stage and the XY axis stage. An electrical discharge machining method for a tapered hole, characterized by machining a circular, elliptical, or oval hole having a cross-sectional outline in a trumpet shape by synthesizing a synchronous motion.
"Number 2"
Ci = θi, Xi = Rsinθi, Yi = Rcosθi
"Equation 3"
Ci = θi, Xi = Rsinθi, Yi = Rcosθi + β, where β is a constant.
"Equation 4"
Ci = θi, Xi = Rsinθi, Yi = Rcosθi + qi, where qi is a variable that determines the cross-sectional shape of the hole. 2. The electric discharge machining method for a tapered hole according to claim 1, wherein after the initial hole machining in the direction of the electrode axis parallel to the Z axis, the tilt angle machining and the lateral servo contour machining are sequentially performed. In an electric discharge machining apparatus in which a C-axis table on which a workpiece is placed, an XY-axis stage, and a Z-axis electrode head are synchronously NC controlled
The Z-axis electrode head is provided with an electrode feeding device that performs axial servo feed movement, reciprocating shuttle movement, and positioning movement of the electrode, and a tilting mechanism that tilts the axial direction within a single plane. Point P is attached at an arbitrary distance (R) from the C-axis table center O,
Synchronous motion calculated by the following equation “Equation 2”, Equation “Equation 3” or Equation “Equation 4” of the XY axis stage while causing the electrode feeder to make a reciprocating shuttle motion. The electrical discharge machining apparatus of the taper hole which processes the hole of circular shape, elliptical shape, or oval shape whose outline cross-section becomes a trumpet shape by combining the above.
"Number 2"
Ci = θi, Xi = Rsinθi, Yi = Rcosθi
"Equation 3"
Ci = θi, Xi = Rsinθi, Yi = Rcosθi + β, where β is a constant.
"Equation 4"
Ci = θi, Xi = Rsinθi, Yi = Rcosθi + qi, where qi is a variable that determines the cross-sectional shape of the hole.

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